Following advances in technology, the development of electronic products has been growing rapidly. With a trend that is moving towards lighter, thinner, shorter, smaller and finer products, and increasingly high requirements for the product functions, the corresponding power that is used also becomes increasingly high. With the requirements for smaller size and more power, the concentration of heat generation over the surface of the electronic components will also increase rapidly, and the related heat management issue becomes very urgent to deal with. The aforesaid can be verified by looking at the heat accumulation effects of a high-power chip, such as CPU, VGA card, north/south bridge chip sets, and communication device in a computer. Accordingly, finding a solution for the heat dissipation issue within a limited area in order to ensure that the product functions normally is a crucial technological issue that needs to be solved today as well as a requirement for product commercialization. Due to the good heat conduction ability of traditional heat pipes, they have been widely used in the electronic part cooling, such as in the heat dissipation in the computer CPU. Attaching a wick structure to the entire internal walls of the heat pipe provides the capillary force for the back-flow of the liquid working medium, but the flow resistance inside the wick structure also contributes significantly to pressure drops in the fluid flow. Consequently, there is a significant reduction in performance under certain operating conditions.
In order to increase the heat conduction ability of traditional heat pipes, a loop heat pipe (LHP) has been introduced as a relatively new heat conduction concept. FIGS. 11 and 12 show the operating principles of a commonly-known loop heat pipe, comprising an evaporator (1′), a vapor section (2a′), a condenser (3′), a back-flow section (2b′) and a compensation chamber (1a′). There is a wick structure (1b′) inside the evaporator (1′). There are many grooves (vapor passages) (10′) on the wall of the evaporator (1′) or the wick structure (1b′), as shown in FIG. 12. The basic working principle is as follows: The wick structure (1b′) itself is able to absorb liquid and cause the wick structure (1b′) to be filled with a liquid working medium. When heat is added to the evaporator (1′), the wick structure (1b′) will be heated up as well, and the liquid in the wick structure (1b′) will be evaporated to become vapor and carry away the heat. As the vapor flows along the vapor section (2a′) and arrives at the condenser (3′), the vapor will be condensed to become a liquid, and the capillary force of the wick structure (1b′) will cause the liquid to flow along the back-flow section (2b′) to the compensation chamber (1a′) and arrive at the wick structure (1b′). Consequently a cyclic loop is formed. The driving force for the circulation of the working medium inside the loop pipe comes primarily from capillary force that is generated in the wick structure (1b′). Therefore the capillary force must be bigger than the pressure drop from the flow of the working medium around the different components of the system, in order to ensure the stable operation of the system. This is known as the capillary limit. If the flow caused by the heat input exceeds the capillary limit, a dry out phenomenon will occur in the loop pipe, which results in stultification of the working medium.